This invention relates to a glass forming machine of the press and blow type in which a charge of molten glass is delivered through the open upper end of a parison mold. The neck or finish portion of the mold is located at the bottom end of the parison mold. When the charge of glass is dropped into the mold through the open upper end, the top of the pressing plunger which is to be used to form the glass to the internal shape of the parison mold, is positioned at or adjacent the neck mold. When the charge has been delivered to the parison mold, a baffle will be seated over the top to close off the upper open end of the parison mold. The plunger is then moved vertically upward and by displacement of the glass, the charge will form a hollow parison having the neck portion thereof formed within the lower neck mold. Upon completion of the formation of the parison, the plunger is retracted downwardly out of the interior of the parison and the baffle will be removed from the parison mold. The parison mold will then open, permitting transfer of the parison from the parison mold to a blow mold where the parison will be expanded into its final container shape.
The plungers used to form the interior of the parisons are generally categorized into either narrow-neck or wide-mouth. This characterization actually relates to the diameter of the neck of the container to be formed in relation to its height and volume. A good example of a wide-mouth bottle or jar would be a baby food jar, while a good example of a narrow-neck bottle would be a beer or beverage bottle.
U.S. Pat. No. 2,289,046 issued to G. E. Rowe describes what is termed an "I.S. Machine" and the three modes of its operation, with the most pertinent for the present disclosure being that shown on sheet 6 of the drawings accompanying this patent, in which a narrow-neck plunger operation is illustrated and the cycle of operation of the narrow-neck press and blow bottle forming cycle is shown.
An example of a wide-mouth press and blow operation is that of U.S. Pat. No. 3,024,571 issued to Abbott et al., and commonly assigned with the present case. In the Abbott et al., patent, the parison mold is described as being a one-piece mold, in that it is not split down the center; however, this is a practice which may be carried out when the parisons are of a wide-mouth type, since the mold may be stripped vertically upward off of the parison as it is held by a neck mold. In a narrow-neck parison forming situation, such as that specifically illustrated in this case, it is necessary that the parison mold be vertically split so that the two halves can be parted freeing the parison for inversion and transfer to a blow mold by the neck and neck mold thereof.
In the operation of a plunger mechanism for moving the plungers in and out of pressing position relative to a parison mold, it has been the practice in the past to use dual pneumatic motors such as that shown in Abbott et al., in FIG. 12, fluid under pressure being fed to the cylinders beneath the pistons thereof to advance the plungers into upward pressing position and upon retraction, air under pressure or fluid under pressure is introduced to the upper ends of the cylinders to reverse the movement of the plungers.
It was found necessary to have dual pistons in order to provide sufficient speed so as to perform the pressing function within the confines of the time element permitted for the formation of the parisons. It should be kept in mind that glass forming machines, such as those described above and termed "I.S. Machines" or "Individual Section Machines" have all of the functions of the machine timed and programmed into a repeating cycle. In order to move the plunger upward into pressing position in a short period of time, it was found necessary to increase the size of the piston or when space would not permit, such as when plural parisons are being formed, it was necessary to provide dual pistons of smaller diameter to effect the same speed of pressing and a consequent increase in force would result.
When considering narrow-neck pressing, such as that illustrated, it has been found desirable that these plungers which are relatively long and slim be operated at low pressing pressure in order to get the required low pressing force. However, when operating at low pressure, the motors that are used will operate at relatively slow speed. Once the parisons have been formed, the plunger is to be retracted with the most expeditious movement possible.